Conventional flexible substrates on which electrodes are disposed have been widely used in piezoelectric devices. Examples of such a substrate include a flexible printed wiring board as disclosed in Patent Document 1. Such a flexible printed wiring board is provided with an electrode thereon including a wide part and a narrow part. The flexible printed wiring board is attached to the housing of an electronic device while being bent. Thus, in the flexible printed wiring board, a bending load is likely to be applied at the boundary between the wide and narrow parts of the electrode and likely to generate cracks.
To avoid this, in the flexible printed wiring board disclosed in Patent Document 1, the boundary is covered and reinforced with a coverlay. With this configuration, generation of cracks is suppressed at the boundary between the wide and narrow parts of the electrode in the flexible printed wiring board disclosed in Patent Document 1.
Patent Document 1: Japanese Patent Application Laid-Open No. 2006-66772